It is desirable for metal layers used for metal lines on semiconductor devices to be compatible in various structured forms. To increase the density of devices formed on a semiconductor substrate, a metal layer can be formed as a multi-layered structure. The metal layer can include, for example, aluminum or tungsten. However, the specific resistance of aluminum is about 2.8×10E-8Ωm and the specific resistance of tungsten is about 5.5×10E-8Ωm. Thus, aluminum and tungsten are typically unsuitable for a multi-layer structure. Consequently, copper, which has relatively low specific resistance and good electromigration characteristics, is often used as a metal layer of a multi-layered structure.
Copper can exhibit a very high mobility when compared to silicon and silicon oxide. However, copper can easily be oxidized when it reacts with silicon and silicon oxide. Accordingly, it may be desirable to suppress the oxidization of copper by using a barrier metal layer.
A titanium nitride layer has been used as a barrier metal layer. However, the titanium nitride layer may not be suitable as a barrier metal layer for copper where the titanium nitride layer is desired to have a thickness above 30 nm to restrain the mobility of copper. Since the titanium nitride layer has a resistance proportional to the thickness thereof and a high reactivity, the resistance may be highly increased when the titanium nitride layer has a thickness above 30 nm.
For at least this reason, a tantalum nitride layer is suggested for the barrier metal layer where a tantalum nitride layer may restrain the mobility of copper even when the tantalum nitride layer is thin and has low resistance. Additionally, the tantalum nitride layer may exhibit a suitable step coverage characteristic and a suitable gap-filling property so that the tantalum nitride layer can also be used as a metal plug, a metal wiring, a metal gate, a capacitor electrode and/or the like, in addition to the barrier metal layer. Examples of tantalum nitride layers that can be used as barrier metal layers are disclosed in U.S. Pat. No. 6,204,204 (issued to Paranjpe et. al.), U.S. Pat. No. 6,153,519 (issued to Jain et. al.), and U.S. Pat. No. 5,668,054 (issued to Sun et. al.).
According to the disclosure in U.S. Pat. No. 5,668,054, the tantalum nitride layer is deposited through a chemical vapor deposition process by using terbutylimido-tris-diethylamido-tantalum ((NEt2)3Ta═Nbut, hereinafter simply referred to as “TBTDET”) as a reactant. The process is carried out at a temperature above about 600° C. If the process is carried out at a temperature of about 500° C., the specific resistance of the tantalum nitride layer may exceed 10,000 Ωcm. In addition, since the above process is carried out at a relatively high temperature, the semiconductor device can be thermally damaged. Further, it can be difficult to achieve a tantalum nitride layer having the desired step coverage when a chemical vapor deposition process is used.
Recently, an atomic layer deposition (ALD) process has been suggested as a substitute for the chemical vapor deposition (CVD) process. The atomic layer deposition process can be carried out at a relatively low temperature as compared with a conventional thin film forming process and can achieve superior step coverage. Examples of the atomic layer deposition processes for depositing tantalum nitride are disclosed in U.S. Pat. No. 6,203,613 (issued to Gates) and in an article by Kang et al., entitled “Plasma-Enhanced Atomic Layer Deposition of Tantalum Nitrides Using Hydrogen Radicals as a Reducing Agent,” Electrochemical and Solid-State Letters, 4(4) C17–19 (2001). As described in the Kang et al. article, a tantalum nitride layer having a specific resistance of about 400 cm, can be formed by an atomic layer deposition process using TBTDET. The deposition is carried out at a temperature of about 260° C. Accordingly, a thin film having a low specific resistance can be formed at a relatively low temperature. In addition, a hydrogen radical obtained by a plasma-enhanced process is used as a reducing agent. Therefore, a power source is applied into a chamber when the deposition is carried out. For this reason, the process described by Kang et al. presents process parameters that may be influenced by the power source applied to the chamber. Thus, while the Kang et al. process can be used to form a thin film having a low specific resistance at a relatively low temperature, the process parameters, which include control of the power source, are added. Moreover, because the Kang et al. process applies the power source directly to a predetermined portion of the chamber to which a semiconductor substrate is placed, the semiconductor substrate can be damaged by the power source.
An ALD process using a tantalum chloride (TaCl5) source in tantalum nitride (TaN) thin film deposition is disclosed in an article by Mikko Ritala et al. entitled “Controlled Growth of TaN, Ta3N5 and TaOxNy Thin Films by Atomic Layer Deposition,” Chem. Mater. 1999, 11, pp1712–1218. Additionally, a CVD process using a TBTDET source in TaN thin film deposition is disclosed in an article by Tsai MH et al. entitled “Metal organic chemical vapor deposition of Tantalum Nitride by Terbutyl-imidotris (Diethylamido) Tantalum for Advanced Metallization,” Applied Physics Letters, V. 67 N. 8, 19950821.
However, the conventional TaN deposition process can exhibit several potential problems due to the potential problems associated with the sources. For example, the TaCl5 source is generally a halogen source, and the halogen source is a solid state and has a high melting point. Therefore, when the TaCl5 source is employed for the deposition process, particles can be generated and impurities, including chloride, may remain on the deposited TaN thin film which can induce additional problems. When a TBTDET source is used for the depositing process, the deposition rate can be too slow because of a low vapor pressure.
Japanese Laid-Open Patent No. 2002-193981 discloses a method of preparing tertiary amyl imido-tris-dimethylamido tantalum (Ta(NC(CH3)2C2H5)(N(CH3)2)3, (hereinafter simply referred to as “TAIMATA”) and a metal organic CVD (MOCVD) process using a solution including TAIMATA as a precursor. According to the method disclosed in Japanese Laid-Open Patent No. 2002-193981, 1 mole of TaCl5, 4 moles of LiNMe2 and 1 mole of LiNHtAm are reacted in an organic solvent at room temperature. The reaction product can be filtered and the solvent used can be removed to prepare TAIMATA. This material can be dissolved into an organic solvent, such as hexane, and thus, the solution obtained can be deposited onto a substrate in a CVD room to form a TaN thin film.
According to the above-described method, however, since the TaN thin film is formed by using only TAIMATA, the formation of the TaN thin film may be uncertain even though the preparation of TAIMATA may be advantageously carried out. When the deposition process is carried out onto the substrate by the CVD process using only TAIMATA, the vapor pressure may not be high enough and the process can be ineffective.